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The Fat Man is perhaps the most devastating infantry weapon ever unleashed upon the modern battlefield - a hand-held catapult that launches portable nuclear bombs.— VDSG Catalogue No.9716

The M42[1] Fat Man is a weapon in Fallout 4.


First entering service in September 2077 with the U.S. Army, the Fat Man is a shoulder-mounted mini nuke launcher. The variant appearing in Fallout 4 has a slightly different appearance than in previous games. There is no longer a handle on the right side of the launcher, and instead two straight handles on the bottom. It also appears to be larger, with a rusted silver paint job.

Developers struggled to find a way to fire the heavy ammunition from a man-portable system far enough to keep the operator outside the blast radius, losing a lot of people in the process. Eventually, it was discovered that by placing a small sub-charge into the ammunition itself, similar to bullets being fired from a gun (or perhaps more accurately described as being along the lines of a recoilless launcher), the warheads could be launched a considerable distance without adding too much weight to the already heavy weapon.

The Fat Man fires in a parabolic arc, with mini nukes being launched approximately 20 yards before impact when held level to the ground on even terrain, requiring it to be angled upward for any distance outside of this range. When fitted with the MIRV launcher, it fires six mini nukes in a cluster that separates in mid-air, drastically reducing its range, but increasing its overall damage and area of effect.

Weapon modifications

ModDescriptionWeapon prefixDamage per shot changeFire rate changeRange changeAccuracy changeMagazine capacity (shots per reload) changeWeight changeWeapon value change in capsEffect(s)Perk(s) requiredComponentsForm ID
Standard launcherStandard.Adhesive x4
Aluminum x6
Gears x6
Nuclear material x4
Screw x5
Spring x6
Steel x9
MIRV launcherAn experimental modification.Experimental MIRV-450+5.3+138Gun Nut: 4
Science!: 4
Adhesive x9
Aluminum x11
Circuitry x5
Gears x8
Nuclear material x6
Screw x8
Spring x7



  • ArcJet Systems - Found in the room marked '2' in the Engine core.
  • BADTFL regional office - In the evidence locker.
  • Boston Airport - Slightly north of Boston Airport, there are wrecked cars. Inside one is a Fat Man. From the Boston Airport fast travel location, head east. The Fat Man is located in a van on the water's edge behind the nose section of an airplane.
  • Boston mayoral shelter - Beneath the basketball court is an entrance to a cave. The Fat Man lies next to a dead soldier at the end of the cave. There is a nearby deathclaw that will attack on sight.
  • Cabot House - In the basement near Edward's bed.
  • D.B. Technical High School - At the far end of the old swimming pool in the northwest corner of the lowest level of the school. This is by the raider boss' bed and terminal.
  • Federal ration stockpile - In the main stockpile area, just inside the room with two turrets against the wall near the terminal that operates the doors (the second one). This Fat Man also respawns.
  • Fort Hagen - In the armory.
  • Goodneighbor - Found behind the desk, beside KL-E-0 in the Kill or Be Killed store.
  • Gunners plaza - In a locked utility closet in the southwest corner of the second floor.
  • Hub City Auto Wreckers - Carried by a named Gunner, Bridget.
  • Lexington - On the walkway where the raider with the power armor is found.
  • Libertalia - Carried by a random raider at the top of the main building.
  • Malden center - Found behind a train car hugging a wall.
  • Outpost Zimonja - Carried by a raider in power armor named Boomer.
  • Quincy ruins - Being held by Sergeant Baker, who is located on top of the church in the ruins.
  • Revere satellite array - Can be found at the top of one of the towers, next to a power armor frame and a case with miscellaneous ammo and other items.
  • Robotics disposal ground - Found laid on top of a car hood near the back of the scrapyard.
  • Salem - On a shelf in a bombed-out store across from the chapel.
  • Spectacle Island - On the lower level of the beached tugboat containing the generator.
  • The Castle - Found in the armory on a shelf, next to it will be a mini nuke.
  • The Prydwen - Inside Proctor Teagan's store.
  • Zephyr Ridge Camp Far Harbor (add-on) - Carried by a Trapper on the tower's top level.


  • There is a chance that a mini nuke fired by the Fat Man will be a dud and cause physical damage instead to the target if hit by the dud.[2]
  • Technical documentation and holotapes found in Fort Strong reveals the Fat Man's pre-War designation: "The M42 Fat Man."
  • When fired from a long enough distance, the projectile makes a loud whistling noise (similar to the cartoon noise for falling from the sky or the sound that bombs make after being dropped) which indicates one should get to cover.
  • The range of the Fat Man is very close to the game engine's near clip loading distance. Mini nukes that travel far enough from the player, can vanish without detonating correctly. This is especially noticeable when firing long distance from a high elevation to a low elevation.
  • When firing with the experimental MIRV modification, there is a chance that it will detonate right at one's feet, even if they are firing away from themselves. This most often happens when the player fires in a direction lower than their current position. This is due to the way the game engine spawns child[3] projectiles.
  • During the first scene of the game, the player character can see an advertisement for the Fat Man playing on TV.
    • This same advertisement for the Fat Man was a promotional advertisement for Fallout 3.
  • Despite Elder Maxson stating that the Fat Man is an essential part of the Brotherhood arsenal, BOS soldiers never use them.
  • When displaying damage on a target's health bar, only the physical impact damage is displayed.
  • In survival mode, mini nukes weigh in at 12 units each in addition to the Fat Man's 30+.

Behind the scenes

"Fat Man" is the codename for the type of nuclear bomb that was detonated over the Japanese city of Nagasaki by the United States on 9 August 1945.


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  1. General Brock's terminal in Fort Strong and Private Murnahan's holotape found in Fort Strong refer to the Fat Man as an "M42 nuclear catapult"
  2. Ten things we've learned about Fallout 4 - Tech Radar (dead link)
  3. Within the Creation Kit, child refers to projectiles which are spawned from explosives.